The invention relates to improvements in methods of and in apparatus for perforating webs of wrapping material for rod-shaped smokers' products More particularly, the invention relates to improvements in methods of and in apparatus for perforating wrapping material with pulsating beams of high-energy radiation, such as laser beams. Still more particularly, the invention relates to improvements in methods of and in apparatus for perforating moving webs or discrete sections of cigarette paper, imitation cork and/or other wrapping material for plain or filter cigarettes, filter rod sections and/or other rod-shaped articles of the tobacco processing industry.
It is well known to provide the wrappers of rod-shaped articles of the tobacco processing industry with perforations which form so-called ventilation zones and serve to admit cool atmospheric air into the column of tobacco smoke flowing from the lighted end of the article toward the mouth of the smoker. As a rule, or at least in many instances, the wrapping material consists of or contains paper and the ventilation zones are formed by puncturing the wrapping material by mechanical means, by electric sparks or by beams of high-energy radiation. The perforating operation can be carried out upon a web of wrapping material or upon the tubular wrappers of discrete rod-shaped articles. If the articles are filter cigarettes, the perforations are normally provided in the region at the junction of the filter tip with the tobacco-containing portion of the article.
The provision of ventilation zones in the wrappers of rod-shaped articles of the tobacco processing industry, such as filter cigarettes, is considered to be of great importance. Thus, cool atmospheric air which is admitted into the column of hot tobacco smoke by way of perforations in the wrapper exerts a beneficial influence upon the percentages of nicotine and condensate in tobacco smoke. In order to ensure that the nicotine and condensate contents of tobacco smoke will be maintained within the prescribed range, it is important to carry out the perforating operation with utmost care, i.e., the ratio of cool atmospheric air, which is drawn into the column of hot tobacco smoke from the atmosphere by flowing through the perforations of the ventilation zone, to the quantity of smoke in a particular brand of rod-shaped smokers' articles should remain at least substantially constant. In other words, such ratio should be the same for each of a short or a long series of articles.
Mechanical perforating apparatus normally employ sets of pins, needles or analogous puncturing elements which are caused to pierce selected portions of a continuous web or of discrete sections of wrapping material for cigarettes or the like. Reference may be had, for example, to U.S. Pat. No. 4,090,826 granted May 23, 1978 to Alfred Hinzmann. A drawback of mechanical perforating apparatus is that the puncturing elements are subject to extensive wear which entails a change in the size of holes if the puncturing elements are not replaced or treated at frequent intervals. In addition, such apparatus are not overly reliable when the speed of advancement of wrapping material reaches a first range and they are incapable of properly perforating a wrapping material when the speed of advancement of such material is within a second range which is required in presently known modern high-speed cigarette making and like tobacco processing machines. Reference may also be had to published German patent application No. 19 01 384.
Published German patent application No. 27 51 522 discloses a perforating apparatus which employs a laser. The impulse sequence of the laser is synchronized with the movement of the material or article to be perforated in order to ensure that the ventilation zone (formed by a number of perforations which is necessary to ensure the admission of a requisite amount of fresh atmospheric air) will be provided at the desired location as considered in the longitudinal direction of a rod-shaped article. Such apparatus are quite satisfactory when the articles are produced at a relatively low rate or even at a higher rate but still below the rate of output of a modern high-speed cigarette making or filter tipping machine. The predictability of the locations of ventilation zones as well as of the permeability of the perforated portions of wrappers of cigarettes or like rod-shaped articles ceases to be satisfactory when the presently known perforating apparatus which employ lasers are utilized in modern high-speed machines for the making of rod-shaped articles of the tobacco processing industry.